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Home , Barium borate

United States Patent (19. 11 Patent Number: 4,897,249 Ross et al. 45 Date of Patent: Jan. 30, 1990

54 PREPARATION by Direct Conversion of Oxides or Hydroxides (75) Inventors: Sidney D. Ross, Williamstown; of Metals. Manuel Finkelstein, North Adams, Chemical Abstracts, vol. 74, No. 24, 131090e, Physico both of Mass. chemical Study of a - Water System at 30. 73) Assignee: Sprague Electric Company, North E. M. Levin and H. F. McMurdie, "The System Adams, Mass. BaO-B2O3', J. Am. Ceram. Soc. 32, 99 (1949). (21) Appl. No.: 332,316 O. Yamaguchi, K. Tominaga and K. Shimizu, “Forma tion and Transformation of Alkoxy-Derived BaB2O4' (22 Filed: Apr. 3, 1989 Ceramurgia Int., vol. 6(3), pp. 103-105 (1980). 51 Int. Cl." ...... C01B 35/12; C01B 15/12; C04B 35/46; C04B 35/48 Primary Examiner-Robert L. Stoll 52 U.S. Cl...... 423/280; 423/279; Assistant Examiner-Lori F. Cuomo 501/137; 501/139 58) Field of Search ...... 423/279, 280; 501/137, 57 ABSTRACT 501/139 A filtered solution of barium hydroxide octahydrate (56) References Cited reacted with an aqueous solution of boric acid to pro vide hydrated y barium borate having a barium to U.S. PATENT DOCUMENTS boron ratio of 1:2 and having fine particle size. The 4,683,126 7/1987 Inoue et al...... 423/280 hydrated y barium borate was converted to the anhy 4,766,027 8/1988 Burn ...... 427/44 drous y form at about 300 to 400° C. Further heating to FOREIGN PATENT DOCUMENTS about 600' to 800° C. converted the product to g-BaB 2O4. The conversion to the 3-form is preferably during 220950 4/1985 German Democratic Rep. . sintering of a dielectric composition to which 47-21397 10/1972 Japan ...... 423/280 the y-BaB2O4 has been added as a . OTHER PUBLICATIONS Chemical Abstracts, vol. 103, No. 26, 216382u, Metal 2 Claims, No Drawings 4,897,249 1. 2 and the insoluble solid was filtered off by gravity using BARIUM BORATE PREPARATION Whatman #1 filter paper. This filtration effectively separated the insoluble barium carbonate that was pres BACKGROUND OF THE INVENTION ent from the soluble barium hydroxide. This invention relates to the preparation of barium 5 An aliqout of the filtrate was titrated with 0.1N hy borate of a fixed barium to boron ratio for use in ce drochloric acid, and the solution was found to contain ramic dielectric compositions, and more particularly to 0.6075 mole of barium hydroxide. A hot solution of such a barium borate for use as a flux in boric acid (75.12 g; 1.215 mole) in 600 ml. of distilled dielectric compositions for ceramic capacitors. water was poured rapidly into the hot, stirred filtrate, Barium borate (BaB2O4) is used in some barium tita 10 and a white precipitate formed. After standing over nate ceramic formulations as a flux so as to lower the night at room temperature the white solid was filtered sintering temperature and maximize the density of the with suction and dried at 120° C. to a constant weight. ceramic. BaB2O4 is usually added in amounts of approx The yield of dried product was 126 g. imately 2% of the total ceramic composition. The effec The titration of the barium hydroxide solution used in tiveness of BaB2O4 as a flux is strongly dependent on the 15 the preparation of BaB2O4 above is tedious. In many barium to boron ratio. Only with strict control of this experiments the titer consistently fell between 94% and ratio can reliably reproducible results be guaranteed. 96% of the weighed barium hydroxide. It is possible to Barium borate has been prepared in the prior art: by assume that the starting hydroxide contains only 5% of the solid state reaction of boric acid with either barium insoluble barium carbonate and 95% of the soluble bar nitrate or barium carbonate; by the reaction of boric 20 ium hydroxide. This makes it possible to omit the titra acid with ; by the simultaneous hydro tion. This simplification can be further justified, since lysis of barium and boron alkoxides; and, by the reaction the of y-BaB2O4, compared to boric acid and of barium chloride with borox. None of these prior art preparative procedures guarantees stoichiometry con barium hydroxide, is such that only y-BaB2O4 will pre trol and none assures that the product will be uniquely 25 cipitate even when either boric acid or barium hydrox BaB2O4, with a Ba to B ratio of 1:2. ide is in excess when the two aqueous solutions are Attempts to control the barium to boron ratio of mixed. These fortuitous solubility relationships, there barium borate to 1:2 by pyrolyzing crystalline organic fore, guarantee stoichiometry control during this prepa precursors have not been successful. Boric acid is ration of y-BaB2O4. known to form coordination compounds from appropri 30 In illustration of the above we cite an experiment in ately substituted diols and hydroxy substituted diols and which a large excess of barium hydroxide was used. hydroxy substituted carboxylic acids. However, recrys Barium hydroxide octahydrate (50 g.; 0.1585 mole) was tallization and pyrolytic decomposition of several of the boiled with 250 ml. of distilled wter. The solution was more promising organic compounds (viz.: barium boro filtered through Whatman #1 filter paper, and the solid di-salicylate; barium-boro-di-O,O'-biphenolate trihy 35 on the filter paper was washed with an additional 25 ml. drate; barium boro-tri-2,3-naphathalenediolate trihy of hot distilled water. Assuming the presence of 95% drate; barium boro-di-pyrocatecholate trihydrate) failed hydroxide this solution should provide 0.1506 mole of to provide BaB2O4. In all four cases the product ob barium hydroxide. A hot solution of boric acid (11.54 g; tained was contaminated by the presence of trace 0.1867 mole) in 75 ml. of distilled water was added to amounts of Ba2B2O2, in which the Ba to B ratio is 1:1 the above barium hydroxide. This represents an enor rather than 1:2, probably due to volatilization of some mous excess of barium hydroxide, since 0.1506 mole of boron as an organo-boron compound during the pyroly the hydroxide would require 0.3012 mole of boric acid sis. In addition the pyrolysis always left some residue of rather than 0.1867 mole of boric acid actually used for unoxidized carbon in the product. complete conversion of the barium hydroxide toy-BaB 45 2O4. When worked up as described in the first prepara SUMMARY OF THE INVENTION tive procedure, the experiment yielded 17.7 g of y In accordance with this invention, barium borate BaB2O4, with stoichiometry maintained at 1 Ba to 2 B. having the barium to boron ratio of 1:2 was obtained by Both y-BaB2O4 and 6-BaB2O4 have characteristic reacting an aqueous solution of boric acid with a barium infrared spectra, which may be used for purposes of hydroxide compound and precipitating the reaction 50 identification. A more precise and more detailed struc product. The reaction of boric acid with barium hy tural identification comes from powder X-ray diffrac droxide octahydrate in water provided the y-form of tion studies which distinguishes y-BaB2O4 from 6-BaB BaB2O4 directly, and provided that product with com 2O4 and both of these products from other members of plete control of the desired stoichiometry and with the system BaO-B2O3. considerable control over the particle size of the prod 55 Additional and unexpected benefit of the above de uct as well. As originally obtained by precipitation from scribed preparative procedure results from the facts that boiling water the BaB2O4 product is hydrated and this the solubility relationships and rates of crystal growth water of hydration is not completely removed by air and crystal precipitation are such that the product is drying at 120. By heating at either 300° C. or 400° C. obtained in fine particle size and with a narrow particle this hydrated y-BaB2O4 was converted to the anhy 60 size distribution. The documentation for these asser drous product, and by further heating at temperatures tions is in the form of electron micrographs and X-ray of 600-800 the y-form was quantitatively converted to diffraction patterns. R-BaB2O4. We note finally that it is a real benefit that the prod DESCRIPTION OF THE PREFERRED uct as initially precipitated is slightly hydrated y-BaB 65 2O4, and that the dehydrated y-BaB2O4 can be obtained EMBODIMENTS by heating at 300-400° C. For use as a flux in ceramic Barium hydroxide octahydrate (Ba(OH)28H2O) (200 formulations it is really not necessary to calcine at g; 0.634 mole) was boiled with 1 liter of distilled water, 600-800° C. to converty-BaB2O4 to 6-BaB2O4. The 4,897,249 3 4. y-form can be used directly in the ceramic formulation, water, precipitating the reaction product of hydrated since the final firings will be at temperatures well in excess of 800 C., and conversion of the y-form to the ty-BaB2O4 having a barium to boron ratio of 1:2 from As-form will take place during that treatment. said water, converting the hydrated product to anhy We claim: 5 drous y-BaB2O4 at 300 to 400 C., and converting the 1. A process for preparing barium borate, said process anhydrous product to 6-BaB2O4 at 600 to 800° C. consisting essentially of obtaining a purified filtrate of 2. The process of claim 1 wherein said converting of soluble barium hydroxide by boiling barium hydroxide said anhydrous product to 6-BaB2O4 takes place during octahydrate in water and filtering off any insoluble sintering of a barium titanate dielectric composition in material, reacting an aqueous solution of boric acid with 10 which said anhydrous y-BaB2O4 is present as a flux. said purified barium hydroxide compound in boiling sk k sk

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